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At least 199 records · Page 11Linked to original sources
PubMed1987

Dependence of erythropoietin production on blood oxygen affinity and hemoglobin concentration in rats.

Plasma erythropoietin titers (Ep) were compared in rats subjected to different kinds of systemic hypoxia. Ep increased exponentially, when hypoxia was induced by exposure to simulated altitude (from less than 0.025 IU Ep/ml plasma at sea-level up to 3.65 IU Ep/ml at 7000 m). An acute increase in the O2 affinity of blood augmented Ep production in normal rats but not in rats exposed to hypobaria. Ep also rose exponentially when isovolemic anemia was induced (e.g., 0.5 IU Ep/ml plasma were found at 7 g Hb/dl blood). When the same reduction in blood O2 carrying capacity was produced by CO-inhalation (0.1% CO in air), Ep increased to 5.57 IU/ml plasma. This very high value was considered to be partly due to the very high O2 affinity of carboxyhemoglobin. These results indicate that a left shift in the hemoglobin-O2 dissociation curve produces a stimulation of Ep production, particularly, when the O2-carrying capacity of blood is lowered.

Anemia↗
PubMed2002

Seasonal variation in the niche, habitat availability and population fluctuations of a bivoltine thermophilous insect near its range margin.

We investigated the niche requirements of the summer and autumn/spring generations of the bivoltine butterfly, Polyommatus bellargusRott., and their implications for population dynamics at sites occurring near its northern range margin. The larvae of this species are sedentary, and the turf height and shelter of Hippocrepis comosa foodplants selected for egg-laying accurately predict larval distributions within United Kingdom (UK) sites. We found a significant shift between the plants used for egg-laying in each generation, with the niche occupied by summer-feeding larvae being broader and different to the autumn one. Measurements of soil temperature confirmed that the short, sheltered foodplants selected by ovipositing females in autumn placed the autumn/spring-feeding generation of larvae in the warmest available microclimates within sites. In late spring, egg-laying females avoided the hottest spots but extended egg-laying into taller, less sheltered (relatively cool) turf where the microclimate was similar to that experienced by autumn/spring-feeding larvae. Using each generations' definition of niche requirement, we analysed surveys of foodplant populations available on 24 UK sites for P. bellargus, and estimated that nearly twice as many plants were available to the summer-feeding larvae compared to those feeding in the autumn. Annual adult population counts match these seasonal differences in site carrying capacity; first generation counts (from autumn-laid eggs) were generally half as abundant as in the second generation, and more variable. These results suggest that the seasonal cycle of niche switches represents an annual (autumn-spring) bottleneck for populations of this butterfly at its northern range margin. Under climate warming we predict that the inter-generational difference in niche availability, carrying capacity and population size will be reduced. We recommend revised management requirements for this threatened species under current and predicted climates in northern Europe.

Animals↗
PubMed1991

Effect of the tibial cut on subsidence following total knee arthroplasty.

In 33 total knee arthroplasties (TKAs) using instrumentation designed to cut the tibia with 0 degree posterior slope, ten tibial components demonstrated at least 2 mm of tibial component subsidence. These subsided components were implanted onto tibiae with an average of 8 degrees +/- 2 degrees difference between the preoperative, anatomic posterior slope and their postoperative posterior slope. The remaining 23 components, without subsidence, were implanted onto tibiae cut within 2 degrees +/- 2 degrees of their anatomic slope. To help understand these clinical observations, a laboratory study was performed to compare the load carrying capacity and the stiffness of tibial subchondral bone following two types of tibial cuts: one made perpendicular to the long axis of the tibia and the other made parallel to the articular surface of the tibia. Mock tibial baseplates mounted on paired cadaver tibiae were loaded in compression and force displacement curves were recorded. Tibiae cut parallel to the surface exhibited 40% greater load carrying capacity and 70% greater stiffness than the paired tibiae cut perpendicular to the long axis. The biomechanical data of this study indicated that cutting the tibia perpendicular to the long axis results in weaker bone that may be inadequate to support a tibial component. This may explain the higher incidence of clinical subsidence if the tibial cut is not made approximately parallel to the anatomic slope.

Aged↗
PubMed2005

[Preparation and characterization of nanoemulsion].

AIM: To prepare nanoemulsion-encapsulated BSA-FITC (NEBSA-FITC), study its characteristics, and measure its uptake by dendritic cells (DCs) and peritoneal macrophages. METHODS: NEBSA-FITC was prepared by a method of interfacial polymerization.The encapsulation rate, drug-carrying capacity and stability of the nanoemulsion were determined by Sephadex-G100 chromatography. The shape and size of NEBSA-FITC were observed under electron microscope. The uptake of NEBSA-FITC by DCs and macrophage cells was detected by FACS and laser confocal microscopy. RESULTS: The mean size of NEBSA-FITC was (25+/-10) nm. The encapsulation rate was 91%, the drug-carrying capacity was 0.091 g/L and NEBSA-FITC had a good stability. The FACS analysis showed that DCs and macrophage cells could take in more NEBSA-FITC than free BSA. The observation under laser confocal microscope found that NEBSA-FITC was located in the cytoplasm of DCs. CONCLUSION: Nanoemulsion can be efficiently taken by DCs and macrophage cells, and therefore may be promising efficient carrier of APCs-targeted antitumor vaccine.

Animals↗
PubMed2006

Chronic hypoxia and the cerebral circulation.

Exposure to mild hypoxia elicits a characteristic cerebrovascular response in mammals, including humans. Initially, cerebral blood flow (CBF) increases as much as twofold. The blood flow increase is blunted somewhat by a decreasing arterial Pco2 as a result of the hypoxia-induced hyperventilatory response. After a few days, CBF begins to fall back toward baseline levels as the blood oxygen-carrying capacity is increasing due to increasing hemoglobin concentration and packed red cell volume as a result of erythropoietin upregulation. By the end of 2 wk of hypoxic exposure, brain capillary density has increased with resultant decreased intercapillary distances. The relative time courses of these changes suggest that they are adjusted by different control signals and mechanisms. The CBF response appears linked to the blood oxygen-carrying capacity, whereas the hypoxia-induced brain angiogenesis appears to be in response to tissue hypoxia.

Animals↗
PubMed2004

Harvesting in seasonal environments.

Most harvest theory is based on an assumption of a constant or stochastic environment, yet most populations experience some form of environmental seasonality. Assuming that a population follows logistic growth we investigate harvesting in seasonal environments, focusing on maximum annual yield (M.A.Y.) and population persistence under five commonly used harvest strategies. We show that the optimal strategy depends dramatically on the intrinsic growth rate of population and the magnitude of seasonality. The ordered effectiveness of these alternative harvest strategies is given for different combinations of intrinsic growth rate and seasonality. Also, for piecewise continuous-time harvest strategies (i.e., open/closed harvest, and pulse harvest) harvest timing is of crucial importance to annual yield. Optimal timing for harvests coincides with maximal rate of decline in the seasonally fluctuating carrying capacity. For large intrinsic growth rate and small environmental variability several strategies (i.e., constant exploitation rate, linear exploitation rate, and time-dependent harvest) are so effective that M.A.Y. is very close to maximum sustainable yield (M.S.Y.). M.A.Y. of pulse harvest can be even larger than M.S.Y. because in seasonal environments population size varies substantially during the course of the year and how it varies relative to the carrying capacity is what determines the value relative to optimal harvest rate. However, for populations with small intrinsic growth rate but subject to large seasonality none of these strategies is particularly effective with M.A.Y. much lower than M.S.Y. Finding an optimal harvest strategy for this case and to explore harvesting in populations that follow other growth models (e.g., involving predation or age structure) will be an interesting but challenging problem.

Animals↗
PubMed2004

Demography in relation to population density in two herbivorous marsupials: testing for source-sink dynamics versus independent regulation of population size.

We compared demography of populations along gradients of population density in two medium-sized herbivorous marsupials, the common brushtail possum Trichosurus vulpecula and the rufous bettong Aepyprymnus rufescens, to test for net dispersal from high density populations (acting as sources) to low density populations (sinks). In both species, population density was positively related to soil fertility, and variation in soil fertility produced large differences in population density of contiguous populations. We predicted that if source-sink dynamics were operating over this density gradient, we should find higher immigration rates in low-density populations, and positive relationships of measures of individual fitness--body condition, reproductive output, juvenile growth rates and survivorship--to population density. This was predicted because under source-sink dynamics, immigration from high-density sites would hold population density above carrying capacity in low-density sites. The study included 13 populations of these two species, representing a more than 50-fold range of density for each species, but we found that individual fitness, immigration rates and population turnover were similar in all populations. We conclude that net dispersal from high to low density populations had little influence on population dynamics in these species; rather, all populations appeared to be independently regulated at carrying capacity, with a balanced exchange of dispersers among populations. These two species have suffered recent reductions in range, and they are ecologically similar to other species that have declined to extinction in inland Australia. It has been argued that part of the cause of the vulnerability of species like these is that they exhibit source-sink dynamics, and disturbance to source habitats can therefore cause large-scale population collapses. The results of our study argue against this interpretation.

Animals↗
PubMed1988

Evaluation of delivery systems for oxygenated cardioplegia.

The oxygen-carrying capacity of four delivery systems for blood and crystalloid cardioplegia was evaluated: nonoxygenated crystalloid cardioplegia, crystalloid cardioplegia oxygenated with a bubbler system and with a membrane system and, finally, blood cardioplegia delivered by the Shiley-Buckberg system. The nonoxygenated crystalloid cardioplegic solution delivered 0.56 ml of oxygen/dl of solution, the bubbler oxygenating system delivered 3.2 ml/dl and the membrane oxygenating system made available 3.7 ml/dl. Blood cardioplegia delivered 4.2 ml/dl when oxygen-carrying capacity was corrected for the shift in the oxyhemoglobin dissociation curve that occurs with hypothermia. There appears to be no advantage between blood and oxygenated crystalloid cardioplegia with respect to the ability of these solutions to provide oxygen to the myocardium during ischemic arrest. However, the bubbler oxygenating system is superior to the membrane and blood delivery systems in that it could administer cold cardioplegia at any time during the operation. In contrast, the membrane and blood cardioplegia delivery systems both depend on integral heat exchangers which limit the delivery of cold cardioplegia to the period of hypothermia.

Adult↗
PubMedDate not supplied

Methemoglobin levels in smokers and non-smokers.

The authors analyzed the blood of a group of 336 smokers and 336 non-smokers to determine if tobacco smoke, potentially the major source of nitrogen oxide pollution for 40% of the adult population, significantly reduces oxygen carrying capacity as a result of methemoglobin formation. Each blood sample was analyzed for carboxyhemoglobin, methemoglobin, and hemoglobin using an automated spectrophotometer. The mean value of methemoglobin in the smokers did not exceed that in the non-smokers; in fact, the level in the non-smokers was significantly greater. As expected, carboxyhemoglobin levels in smokers substantially exceeded those in non-smokers. The authors conclude that methemoglobin arising from cigarette smoke exposure does not interfere with the oxygen carrying capacity of the blood in smokers.

Carboxyhemoglobin↗
PubMed1978

Generalizing Fisher's "reproductive value": "Incipient" and "penultimate" reproductive-value functions when environment limits growth; linear approximants for nonlinear Mendelian mating models.

In the usual Darwinian case in which struggle for existence leads to density limitations on the environment's carrying capacity, R. A. Fisher's reproductive-value concept reduces to zero for every initial age group. To salvage some meaning for Fisher's notion, two variant reproductive-value concepts are defined here: an "incipient reproductive-value function," applicable to a system's early dilute stage when density effects are still ignorable; and a "second-order penultimate reproductive-value function," linking to a system's initial conditions near equilibrium its much later small deviations from carrying-capacity equilibrium. Also, slowly changing age-structured mortality and fertility parameters of Lotka and Mendelian mating systems are shown to suggest linear reproductive-value surrogates that provide approximations for truly nonlinear diploid and haploid models.

Journal Article↗
PubMed2005

Effects of ecological differentiation on Lotka-Volterra systems for species with behavioral adaptation and variable growth rates.

We study the properties of a n2-dimensional Lotka-Volterra system describing competing species that include behaviorally adaptive abilities. We indicate as behavioral adaptation a mechanism, based on a kind of learning, which is not viewed in the evolutionary sense but is intended to occur over shorter time scales. We consider a competitive adaptive n species Lotka-Volterra system, n > or = 3, in which one species is made ecologically differentiated with respect to the others by carrying capacity and intrinsic growth rate. The symmetry properties of the system and the existence of a certain class of invariant subspaces allow the introduction of a 7-dimensional reduced model, where n appears as a parameter, which gives full account of existence and stability of equilibria in the complete system. The reduced model is effective also in describing the time-dependent regimes for a large range of parameter values. The case in which one species has a strong ecological advantage (i.e. with a carrying capacity higher than the others), but with a varying growth rate, has been analyzed in detail, and time-dependent behaviors have been investigated in the case of adaptive competition among four species. Relevant questions, as species survival/exclusion, are addressed focusing on the role of adaptation. Interesting forms of species coexistence are found (i.e. competitive stable equilibria, periodic oscillations, strange attractors).

Adaptation, Biological↗
PubMed1981

Polycythemia: mechanisms and management.

The principal function of erythrocytes is the transport of oxygen. Erythropoiesis proceeds at a rate consistent with the demand for oxygen-carrying capacity, and the major regulator of erythrocyte production is erythropoietin. Erythropoietin is produced primarily by the kidney under control of a tissue oxygenation sensor. The recently developed erythropoietin radioimmunoassay should provide a clinically useful tool. Erythrocytosis is a pathologic state characterized by an elevated erythrocyte mass, which may result from increased proliferation of erythroid progenitors due to an intrinsic cellular defect or in response to extrinsic signals. Secondary erythrocytosis results from either physiologically appropriate compensation for inadequate tissue oxygenation or from inappropriate stimulation of erythropoiesis. Erythrocytosis increases oxygen-carrying capacity of the blood, but at high hematocrit levels increased blood viscosity may result in decreased tissue oxygen delivery. Polycythemia vera is a hematopoietic stem cell disease of clonal origin. Initial results from the Polycythemia Rubra Study Group suggest that therapy with chlorambucil is associated with an unacceptably high risk for development of acute leukemia, and 32P is preferred for situations in which phlebotomy alone is insufficient.

Blood Gas Analysis↗
PubMed1989

Oxygen binding of modified hemoglobins in solution.

SFHS modified by covalent incorporation of pyridoxal phosphate using NaCNBH3 as reducing agent had P50 values of 21-25mm Hg, and was insensitive to the addition of BPG. The Hill slope of the modified product was 2.34, demonstrating good functional cooperativity of the subunits. Oxygen carrying capacity, calculated as the ratio of O2 content to the concentration of functional hemoglobin, was found to be about 1.3, very close to the "textbook" ratio of 1.34 for whole blood. These values were achieved with oxygen saturation values over 90% and methemoglobin levels of less than 3%. The results obtained from pyridoxalation using NaCNBH3 contrasted sharply with those obtained using NaBH4, which yielded a product having high oxygen affinity and high methemoglobin values. This latter product was poorly saturated with oxygen at ambient pressures and demonstrated a significantly lowered oxygen carrying capacity. The NaBH4 product was also insensitive to the addition of BPG; the reason for this was not ascertained. SFHS-P by the borohydride method thus exhibited marked deficiencies relative to that prepared with cyanoborohydride, as defined by the characterizations employed for this study.

Borohydrides↗
PubMed1983

Intraoperative autotransfusion during abdominal aortic reconstruction.

Intraoperative autotransfusion by a continuous-flow centrifuge system was used during more than 300 abdominal aortic reconstructions at the Cleveland Clinic since May 1979. Fifty consecutive patients undergoing such operations were studied prospectively. Volumes of blood lost, salvaged, and transfused during each operation were tabulated. Autologous autotransfused blood was compared with homologous bank blood with respect to oxygen-carrying capacity, coagulation factors, microaggregate levels, red cell mass, pH, and free hemoglobin concentration. Chromium-51 red cell survival studies were performed in autotransfused blood in random patients and in control subjects. Renal, hepatic, and coagulation functions were determined during the first postoperative week. Each patient received a mean volume of 1,203 ml of autotransfused blood and 1,682 ml of bank blood to replace a mean operative blood loss of 2,386 ml. Red blood cell survival of both salvaged autologous and unshed autologous blood in the control group was nearly identical. Salvaged blood had superior oxygen-carrying capacity, a lower microaggregate level, and better buffering capacity than bank blood. Although transient elevations in liver function values and free hemoglobin levels were noted, no clinically important aberration of coagulation, hepatic, or renal function was demonstrated.

Aged↗
PubMed2000

Anthropological cybernetic model of demography of the island of Hvar.

Intentions of the present investigation were to apply a cybernetic model in description of demography on the island of Hvar for a time period from year 1800 till now. The basic idea of the model applied in this anthropological study (LOPI) is that the rate of reproduction is given by the non-linear controller: Y2/Te(1-(Y3/G)). Constant G represents an environmental carrying capacity of a community with respect to the cohort of older people (no longer a part of the pool of reproductive inhabitants; Y3) sharing limited survival resources. The proportional constant 1/Te connected with the pool of reproductive inhabitants (Y2) correspond to the reproduction maximum. The consistency of the model is evaluated through comparison between model data and census. The LOPI model describes incredibly well the demography of the island of Hvar from the year 1800 till 1940. After year 1950 there were more inhabitants on the island then the model would predict. This fact is connected with changes in the migration or also in the increased carrying capacity (G). On the basis LOPI model, population dynamic oscillates in its development. The example of the island of Hvar has proved that population reaches a maximal number of inhabitants every 200 years. The oscillation of population dynamics is influenced by the migration processes. The mere fact that oscillating population size is connected to population genetics and probably also to sociocultural factors suggests that a cybernetics demographic model can be a guide in the holistic anthropological approach.

Adult↗
PubMedDate not supplied

When are resting water-breathers lacking O2? Arterial PO2 at the anaerobic threshold in crab.

The minimum arterial O2 partial pressure (PaO2) at which, in resting conditions, O2 consumption (MO2) can be maintained and below which anaerobic metabolism is initiated was studied in the crabs Eriocheir sinensis and Carcinus maenas at 15 degrees C. Arterial PO2, MO2 (in E. sinensis), blood lactate concentration ([lact]b) and blood copper concentration ([Cu]b, an index of the blood O2 carrying capacity) were determined after 24 h exposure to inspired PO2 (PIO2) ranging from 2.7-2.1 kPa. They were compared to normoxic controls. In normoxia, the most frequently measured PaO2 ranged between 1 and 3 kPa in both species. In hypoxia, the threshold for blood lactate appearance was PaO2 = 2.1 kPa in E. sinensis and 1.3 kPa in C. maenas, but in many individuals anaerobic metabolism was initiated at lower PaO2's. The lowest PaO2 with [lact]b approx. 0 was 0.7 kPa in both species. MO2 was maintained in 4 E. sinensis out of 6 with PaO2 ranging from 0.7-1.2 kPa (PIO2 = 2.1 kPa). The arterial PO2 at which anaerobic metabolism occurred was not related to blood O2 carrying capacity.

Anaerobiosis↗
PubMed2001

Cadmium binding to a histidine-rich glycoprotein from marine mussel blood plasma: potentiometric titration and equilibrium speciation modeling.

Cadmium-binding parameters (conditional stability constants and carrying capacities) of Mytilus edulis blood plasma histidine-rich glycoprotein (HRG) were investigated by potentiometric titrations using a Cd ion-specific electrode. Titration data were applied to a single-component complexation model and expressed as Scatchard plots that were analyzed using the graphical curve peeling method and the algebraic statistical mechanical method. These sets of binding parameters, derived for the purified HRG, were subsequently entered into the geochemical speciation model MINTEQA2 and then used to simulate the experimental titration, thereby determining which set of log K and CL values best represented the titration data. The Cd binding to HRG was best described by a two-class model with log K values of 7.65 +/- 0.10 and 5.41 +/- 0.06 M-1 and carrying capacities of 6.0 +/- 1.2 and 9.5 +/- 0.4 sites/molecule, respectively. At concentration of total Cd measured in the blood plasma of field-collected mussels (< or = 2 x 10(-7) M), plasma Cd speciation would be dominated by the strong affinity sites of HRG (> 93.5% of total Cd binds to HRG), whereas HRG itself would only be 0.05% saturated with Cd, indicating a high-capacity, apparently nonsaturable Cd transport system.

Animals↗
PubMed2004

Vibration in operating heavy haul trucks in overburden mining.

The objective of this study was to determine if the vibration in sagittal (x), coronal (y) and vertical (z) axes of the seat pan of the heavy haul trucks used in overburden mining, and the vibration experienced by the drivers at the third lumbar and seventh cervical vertebral levels in operating these trucks exceeded the ISO standards, thereby posing threat to safety. A new and an old truck of two different makes and different carrying capacities (200 and 300 series) were instrumented with a triaxial accelerometer on the seat pan. Fourteen drivers (8 male and 6 female) were instrumented with a triaxial accelerometer at C7 and L3 spinous processes. The vibration at the seat pan, C7, and L3 levels were recorded using an onboard computer with PCMCIA card and, compared against the ISO standards. The vertical vibration of the seat pan in the entire sample ranged from a low of .37 m/s2 to a high of 11.73 m/s2. The vibration at the lumbar level in the sample ranged between .34 and 2.72 m/s2. The values for cervical level vertical vibration in the sample ranged between .2 and 2.22 m/s2. The gender of the driver, truck make, and it's carrying capacity did not have a significant effect on the vibration. However, the body weight of the driver, the segment of the truck and the site of measurement revealed significant differences in vibration (p < 0.001). Out of a total 36 combinations (4 trucks x 9 recording locations) the seat pan vertical vibration exceeded the ISO standards 8 times for males and 9 times for females. The lumbar vertebral vertical vibration in males exceeded ISO standards 12 times and in females 11 times. The cervical vertebral vertical vibration exceeded ISO standards once in females only. However, in sagittal and coronal planes the whole body vibration exceeded the ISO standards many times. Heavy haul trucks (240 and 320 ton capacity) frequently generated vibrations in excess of ISO standards in overburden mining operation representing a health hazard.

Adult↗